The present invention relates to a process for producing directly reduced iron (DRI) or other mineral products by directly reducing materials containing iron oxides in a rotary kiln using a solid carbonaceous reducing agent, such as coal, and, more particularly, to a method and means for blowing reducing agent into the discharge end of the kiln in an improved manner.
Many different methods have been suggested and used for carrying out the direct reduction of ores and other materials containing iron oxides using solid carbonaceous materials, particularly coal, in a rotary kiln to produce directly reduced iron (DRI) and other mineral products. For example, in some of these processes the coal is fed into the kiln through the discharge end by mechanical or pneumatic means, such as respectively disclosed in U.S. Pat. No. 3,113,859 to Moklebust and U.S. Pat. No. 3,505,060 to Heitmann, and in some it is fed at the center of or along the kiln, such as disclosed in U.S. Pat. No. 3,206,299 to Senior et al. However, considerable problems have been encountered with these various approaches, many of which problems have been overcome by the process disclosed in U.S. Pat. No. 3,890,138 to Hockin. In this latter process a portion of the coal is injected or blown from the discharge end of the kiln, and the remaining portion of the coal is fed with the ore at the charge feed end. The kiln is generally divided into a reducing zone toward the discharge end and a preheat zone toward the feed end, and the coal is distributed in the kiln in such a manner that the amount of coal injected from the discharge end is sufficient to aid in controlling the temperature profile throughout both zones of the kiln.
Although the process of Hockin was developed particularly for use in reducing ilmenite, it has been found that the dual end feeding technique improves upon the other solid reducing agent feeding methods used in reducing iron-oxide-containing materials in rotary kilns to produce directly reduced iron (DRI) or to produce other mineral products with the direct reduction process, and the present invention relates generally to improvements in the latter processes particularly with regard to the control of the feeding through the discharge end.